Method for producing metallic filaments having a formed skin

ABSTRACT

Filaments composed characteristically of iron, useful for example in reinforcing concrete or the like, are produced by spinning an apertured crucible containing a melt of iron base composition, which includes a reactant agent capable of solid compound formation at the temperature of the melt, subjecting the melt to a pressure in order to cause extrusion of interrupted streams of the melt through the crucible apertures into a reactant gas, and chemically combining the reactant agent and the reactant gas at the surfaces of the filaments so formed in order to provide each individual filament with a traveling mold composed of the solid compound during solidification. This traveling mold, for example, is compatible with concrete or the like for secure bonding.

United States Patent lnventors Appl. No.

Filed Patented Assignee IIarbhajan S. Nayar Waltham, Mass.;

Walter L. Finlay, New York, N.Y.

METHOD FOR PRODUCING METALLIC FILAMENTS HAVING A FORMED SKIN 4 Claims, 2 Drawing Figs.

US. Cl 264/8, 264/82 Int. Cl BOIj 2/04 Field of Search 264/8, 13, 82

0 o 7 O I [5 6] References Cited UNITED STATES PATENTS 3,466,352 9/l969 Corbett 264/8 Primary Examiner-Robert F White Assistant Examiner-J. R. Hall Att0rney-M0rse, Altman & Oates ABSTRACT: Filaments composed characteristically of iron, useful for example in reinforcing concrete or the like, are produced by spinning an apcrtured crucible containing a melt of iron base composition, which includes a reactant agent capable of solid compound formation at the temperature of the melt, subjecting the melt to a pressure in order to cause extrusion of interrupted streams of the melt through the crucible apertures into a reactant gas, and chemically combining the MOTOR reactant agent and the reactant gas at the surfaces of the filaments so formed in order to provide each individual filament with a traveling mold composed of the solid compound during solidification. This traveling mold, for example, is compatible with concrete or the like for secure bonding.

PATENTEnunvz Ian v v 3,617. 587

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SHEET 2 OF 2 AQUEOUS SLURRY CEMENTITOUS MATRIXfiO F l LAM ENTS-48 IRON BASE FILAMENT TITOUS o CED EN L 6 MA'" IAL 4 luvegly'roRs BY If X Wm,Qlim10a/i ATTORNEYS METHOD FOR PRODUCING METALLIC FILAMENTS HAVING A FORMED SKIN BACKGROUND AND BRIEF DESCRIPTION The present invention relates to the production of high tensile strength metallic filaments of relatively short length for use in reinforcing low tensile strength metallic or nonmetallic matrices, and more particularly to devices, processes and products involved in the production of iron base filaments for use in reinforcing cementitious matrices composed of cement, mortar or concrete. It has been found that when a suitable amount, usually'lO to 60 percent and preferably 30 to 60 percent by total weight, of suitably formed iron base filaments (preferably 0.010 to 0.025 inch in diameter and 56 to 1 inch in length) with suitable surface coatings is uniformly distributed in concrete of the like, the volume of concrete needed for a given function is substantially reduced. Thus, under appropriate circumstances, a 6-inch thick concrete road bed may be replaced by l-inch thick concrete, reinforced with iron base filaments. However, difficulties have been encountered in producing short iron base filaments having the chemical composition, geometrical dimensions, high strength, low cost, high corrosion and and erosion resistance, before and during mixing with wet concrete, desirable for effective bonding in the hardened concrete and for practical supply in large quantity for economical use.

The primary object of the present invention is the production of iron base, short filaments by: simultaneously spinning an apertured crucible containing a melt iron or, preferably iron base alloys of certain specified characteristics, and applying to the melt in the crucible a pressure (for example an inert gas or a sufi'icient metallostatic head) in order to cause extrusion of interrupted streams of the melt, i.e., filaments, through the apertures; and controlling the interrupted streams chemically by forming a travelling mold at the surface of each filament, by which the elongated shapes of the filaments are retained while their interior portions are solidifying. Such iron base filaments are useful as a filler in cementitious building materials such as cement, mortar and concrete.

Other objects of the present invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process exemplified in the following detailed disclosure, the scope of which will be indicated in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the nature and objects of the present invention, reference is to be had to the following detailed description, together with the accompanying drawing wherein:

F I0. I is a broken away perspective view, partly schematic and partly cross-sectional, illustrating apparatus for manufacturing filaments in accordance with the present invention; and

FIG. 2. is a flow diagram illustrating, in exaggerated cross section, process steps, an intermediate product and a final product in accordance with the present invention.

DETAILED DESCRIPTION An apparatus constructed for the production of filaments in accordance with the present invention is shown in FIG. I as comprising a rotatable pot 10 for producing filaments and a tray I2 for catching filaments so produced. Pot 10 has a cylindrical cavity I8 which is defined by the cylindrical wall of pot l0 and a plurality of apertures through the cylindrical wall. The top extremity of pot l0 usually is closed to enable the control of pressure of inert gas within cavity 18. In those cases where the top extremity is left open, one must depend upon the ferrostatic pressure developed by the head of molten iron to develop the desired extrusion pressure. Pot I0 is carried axially by the vertical output shaft of an electric motor 20 that is mounted on a stationary rigid base 22. A control circuit for monitoring the rotational speed of the motor shaft is shown at 60. Projecting into the cylindrical cavity 18 of pot 10 are two concentric tubes 62, 64, tube 62 being the inner tube and tube 64 being the outer one. It is to be noted that the axes of pot l0 and tubes 62 and 64 are coincident. Inner tube 62 communicates with the bottom orifice of an induction furnace 66, which is heated by induction coils 68. The temperature of the furnace is controlled by a (not shown) sensor and an electronic circuit 32. Furnace 66 is covered hermetically by a lid 82. Projecting through lid 82 into furnace 66 is a melt flow rate control rod 72, the position of which is monitored by a melt flow rate control circuit 74. Controls 72 and 74 determine the size of the opening of the orifice 80 of furnace 66 and thus the flow rate in order to maintain a constant melt level 86 in pot 10. The melt level 86 is always higher than uppermost aperture 30. Thus molten metal from furnace 66 passes orifice 80 and tube 62 into cavity 18 of pot l0 and finally out through apertures 30 of pot 10 to form filaments 31. A conduit 28 serves to supply inert gas under controlled pressure into pot 10 via conduit 76 and into furnace 68 via conduit 78. Thus the pressure of the inert gas at any given time is the same in furnace 66 as in pot 10. It will be understood that if the metallostatic head in pot 10 is sufficiently high, the high inert gas pressure may be eliminated. Conduit 76 is connected to a junction unit 70 in order to supply the inert gas to cavity 18 of pot 10 via the annular space defined between the walls of tubes 62 and 64. The design of unit 70 is such that it permits rotation of outer tube 64 while it permits inner tube 62 to remain stationary. The inert gas supply is shown at 34 and its pressure control is shown at 36. The filaments extruded through apertures 30 are projected into the gas within tray 12. The composition of the gas is such that it reacts with the moldforming element at the surfaces of the filaments to produce a shape-retaining skin. In the process of FIG. I, the gas is air and the skin is an oxidic compound.

FIG. 2 illustrates a process for producing and utilizing iron base filaments, in accordance with the present invention. As shown in FIG. 2(a), molten iron or iron base alloy metal 38, containing a suitable mold-forming element 40 as an additive, is transferred into a rotating pot 42 that is heated to a temperature slightly above the melt temperature to avoid solidification in pot 42. At the upper surface of the melt is an inert gas such as nitrogen or a noble gas (e.g., argon), the pressure 44 of which is increased. The combination of the inert gas pressure and the centrifugal pressure due to pot rotation forces the molten metal through horizontal holes 46 in the rotating pot. Outside of the pot is open air, into which the molten streams extrude through holes 46. As any component of a molten stream emerges from a hole, it has two velocity components-one in the radial direction (primarily due to inert gas pressure) and the other in the tangential direction (primarily due to the pot rotation). As a result: (1) a chemical reaction occurs, between the additive in the molten stream and oxygen in the air, to produce a solid oxide skin which acts as a mold to retain the linear shape of the molten stream; and (2) the continuity of the molten stream is interrupted due to the centrifugal force which increases with increasing distance from the center of rotation and the shearing force of the molten filamentary stream against the air in the tangential direction. Thus, the controlled inert gas pressure, pot diameter and rotation, and mold forming element combine to ensure iron base filaments characterized by close tolerances in shape and dimension.

The main function of the inert gas pressure is to force the molten metal out of the horizontal holes, thereby imparting a linear velocity to the emerging molten stream. The magnitude of the linear velocity of the stream is related to the inert gas pressure, which preferable ranges from 5 to 500 pounds per square inch above ambient. The purpose of using gas that is inert is to preclude any chemical reaction involving the additive before the liquid metal leaves the pot. [t is to be noted that there is no consumption of inert gas other than to fill the space above the molten metal in the pot.

In a preferred process of the present invention, a solid oxide mold is formed when the mold-forming element in the merging molten stream reacts with oxygen in the air surrounding the pot. The mold-forming element provides a strong, high melting point mold by reacting with oxygen. More generally, the iron base alloy when spun into a specific environment, reacts with that environment to form a suitable traveling mold. Examples of such a mold are found in binary and higher order iron base alloys with Al, Mg, Be, Zr, Si and Ce. Thus, for example, when themold-forming metal is Ce and the external atmosphere is a sulfur containing gas such as S0,, H,S or sulfur vapor, a travelling mold of Ce S, is formed. Alternatively, for example, if the mold-forming element is Al and the external atmosphere is N,, a travelling mold of AlN is formed. Preferably, the iron base composition, by total weight, contains from 80 to 99.9 percent iron and from 20 to 0.1 percent mold-forming element. More preferably the mold forming element is present in the range from 0.5 to l percent by total weight. The mold-forming element should meet the following requirements: (1) It should be miscible with the molten metal; (2) it should have a negative free energy of formation of its mold compound greater than the compound of the molten metal; (3) its mold compound should have a considerably higher melting point, lower vapor pressure, and other characteristics so as to give a strong, continuous, stable and relatively rigid skin for the travelling mold and be wet by the molten metal to give a rigid, stable and adherent skin while the interior of the filament is still molten; and (4) preferably the moldforming element should lower the surface tension of the iron base melt since it appears that, under these circumstances, the mold-forming element tends to concentrate near the surface of the filament and, therefore, is in immediate position to react with the external gas to form the travelling mold and to reduce the tendency of the filament to draw itself into a sphere.

If the pot were to remain stationary and the molten metal were extruded only under the influence of inert gas pressure and stationary mold formation at the filament surfaces, continuous or discontinuous filaments would form depending upon the inert gas pressure, temperature of the molten metal, hole size, concentration of mold-forming element, vibrations in the mold and pulsations in the inert gas pressure. Under such circumstances, extremely close control over such variables has been found necessary in order to obtain discontinuous filaments of controlled length, diameter and uniformity. In order to achieve economy while obtaining discontinuous filaments of controlled length, diameter and uniformity, it is desirable to rotate the pot at between 100 and 800 revolutions per minute with a pot diameter varying from 4 to 8 inches.

The iron and iron base alloy filaments 48 produced in accordance with the specific process hereof are useful for example as a filler for a cementitious construction material, such as cement, mortar or concrete, as shown at 50. Generally, the elastic modulus of such iron compositions is high, ranging approximately from 30 l0 to 40x10? pounds per square inch. Preferably these filaments are needle shaped particles characterized by a diameter ranging approximately from 0.010 to 0.025 inch and length ranging approximately from A to 1 inch in length. Preferably, the iron base filaments are present in the cementitious material in an amount ranging from 30 to 60 percent. A typical concrete of the type shown at 50 is a mixture of water, cement and an aggregate composed of hard inert particles of varying size, such as a combination of sand or brokenstone screenings, with gravel, broken stone, lightweight aggregate, or other material. The cement typically contains, by total weight, approximately: silica (SiO,)- 21.92; alumina (Al O )6.9l; iron oxide (Fe,O,)-2.9l; calcium oxide (CaO)0.82; and residue-remainder. The metal filaments produced as in FIG. 2, without further processing can be blended into the wet concrete. Drying the mixture provides the unusually strong building material shown at 52.

The following nonlimiting examples further illustrate the present invention.

EXAMPLE 1 A melt containing, by total weight, approximately 97 percent iron, 1 percent carbon and 2 percent aluminum is introduced into pot 42 under a protective atmosphere of argon at l00 pounds per square inch. The hole diameter is 0.020 inch, The pot, which has an inside diameter of 8 inches, is rotated at 500 revolutions per minute. The combination of the inert gas pressure and the pot rotation causes extrusion of melt filaments into air. The formation of a filament skin composed of M 0 produces iron alloy filaments which are about 0.0l5 inch in diameter and about h inch in length. The filaments are uniform and are appropriate for mixing into concrete in their initial condition.

EXAMPLE 2 The process of example i is repeated except that the rotational velocity of the pot is approximately 250 revolutions per minute. The resulting filaments now are approximately l-inch long.

EXAMPLE 3 The filaments of example 1 are mixed into wet concrete in the ratio by weight of 40 percent filaments to 60 percent concrete. The wet concrete is hardened to produce a sharply stronger material than would exist in the absence of the filaments.

EXAMPLE 4 A melt containing, by total weight, approximately percent iron and [5 percent aluminum is introduced into pot 42, which has an internal diameter of approximately 8 inches. The melt is under a protective atmosphere at argon at approximately 100 pounds per square inch. The hole diameter is 0.020 inch. The pot is rotated at 500 revolutions per minute. The resulting filaments are approximately 1% inch in length and 0.015 inch in diameter. The resulting filament skin is composed of M 0 The resulting filament skin is composed approximately, by total weight, of iron-85 percent and aluminuml5 percent. The filaments are heated to 600 C. and slowly cooled. As a result, the filament core composition is in the ordered state and, as such, is very strong, having an elastic modulus approaching 40X l 0 pounds per square inch.

EXAMPLE 5 The method of example I is repeated except that the melt contains, by total weight, approximately 88 percent iron, 2 percent carbon and 10 percent silicon, a mixed oxide of iron and silicon being the mold forming agent. The result is a filament skin composition of SiO,.

EXAMPLE 6 The method of example I is repeated except that the melt contains, by total weight, l percent Al and a remainder of iron.

The present invention thus provides processes for the production of iron and iron alloy filaments, products in which such filaments are contained and devices for producing such filaments. Since certain changes may be made in the foregoing disclosure without departing from the scope of the invention hereof, it is intended that all matter described in the foregoing specification and shown in the accompanying drawings be interpreted in an illustrative and not in a limiting sense.

What is claimed:

1. A process for producing iron base filaments of predetermined length, said process comprising the steps of spinning an apertured pot containing a melt of an iron base composition having a metallostatic head, incorporating in said iron base composition a solid skin-forming reactant, applying to said melt a pressure, surrounding said pot with a gaseous reactant, extruding said melt as a stream through apertures in said pot into said gaseous reactant, the combination of said pressure, the diameter of said pot and the rotational speed of said pot causing interruption of said stream to produce filaments, reacting said skin-forming reactant at the surface of said filaments with said gaseous reactant to provide a solid skin about said filaments having a higher melting point than does said iron base composition, and thereafter reducing the temperature of said filaments in order to solidify said iron base composition within said solid skin, said pressure being constituted by said metallostatic head, said iron base composition, by total weight, contains from 80 percent to 99.9 percent iron and from to 0.1 percent of said skin forming reactant, said pressure ranging from 5 to 500 pounds per square inch above am- 

2. The process of claim 1 wherein said skin-forming reactant is aluminum and said gaseous reactant is oxygen.
 3. The process of claim 1 wherein the speed of said spinning is between 100 and 800 revolutions per minute.
 4. The process of claim 1 wherein said gaseous reactant is oxygen. 